ML20134M130
| ML20134M130 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 11/12/1996 |
| From: | Hosmer J COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9611220234 | |
| Download: ML20134M130 (6) | |
Text
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Commonweahh Edison Company 1400 Opus Place Downers Grove, IL 60515-5701 November 12,1996 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 i
Subject:
Response to a Request for Information Regarding Dynamic Testing of Instrument Channels i
Byron Nuclear Power Station, Units 1 and 2 Facility Operating Licenses NPF-37 and NPF-66 NRC Docket Nos. 50-454 and 50-455 Braidwood Nuclear Power Station, Units 1 and 2 Facility Operating Licenses NPF-72 and NPF-77 NRC Docket Nos. 50-456 and 50-457
References:
See Attachment 1 j
j Although instrumentation setpoints and methodology for Commonwealth Edison Company's (Comed's) Braidwood Nuclear Power Station, Units 1 and 2 (Braidwood),
and Byron Nuclear Power Station, Units 1 and 2 (Byron), have been previously reviewed j
and approved by the United States Nuclear Regulatory Commission (NRC) Staff, a concerned NRC Staff member has raised several issues regarding dynamic testing of instrument channels using the MESAC system at Braidwood. These concerns were reviewed by the NRC StaffInstrumentation and Controls Branch (HICB). HICB concluded that the health and safety of the public is not affected by the use of the MESAC system at Braidwood and that Comed is in compliance with its licensing bases and Technical Specifications (TS). Nevertheless, the concerned NRC Staff member requested that Comed review the HICB analyses and conclusions and confirm that Braidwood and Byron are being operated within their licensing bases and TS. That request and abbreviated HICB analyses were transmitted in Reference 1.
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U.S. NRC November 12,1996 A conference call was held on June 21,1996, between Comed and the NRC Staff l
(Reference 2) to clarify the concerns. During the conference call, Comed stated that it agreed with the HICB analyses and conclusions. At the conclusion of the conference call, Comed understood that the heart of the NRC staff member's concern was whether or not the 3 (*10) percent deviation in the lead / lag time constants in the thermal overtemperature AT (OTAT) reactor trip setpoint at Braidwood (Byron) was bounded by the Updated Final Safety Analysis Report (UFS AR) Chapter 15 accident analyses.
For Braidwood and Byron, the OTAT trip function is credited for two UFSAR Chapter 15 accident analyses; uncontrolled rod cluster control assembly (RCCA) withdrawal at power and uncontrolled boron dilution. The uncontrolled RCCA withdrawal at power is more lirniting with respect to departure from nucleate boiling (DNB).
The OTAT trip function at Braidwood and Byron was designed in accordance with WCAP-8745-P-A, an NRC reviewed and approved topical report (Reference 3).
I The following is the OTAT equation described in the Braidwood and Byron TS:
OTAT = AT * {K - K2 *(1 + T4S)/(1 + T3S)[T/(1 + 16S)- T'] + K3(P-P') -f(AI)}
i where AT is indicated AT at Rated Thermal Power and K = 1.325, K2 = 0.0297, i
14 = 33 seconds, is = 4 seconds, and T6 = 0 scconds.
To ensure that the OTAT trip setpoint delay for the trip actuation to be the maximum value,16 is set to 6 seconds in the accident analyses. This added 6 second delay in the accident analyses was to account for any additional or unknown errors such as uncertainty in T4and T5 For the purpose ofillustrating the effect of the lead / lag dynamic term, the above equation can be simplified to perform a sensitivity study since the pressure and f(AI) terms do not have lead / lag or rate functions:
Normalized OTAT trip setpoint = K - K *(1 + T4S)/(1 + T5S)[T/(1 + T6S) - T']
i 2
Figure I shows the normalized OTAT setpoint as a function of time for various t uncertainties while ramping input in over 30 seconds. Case I has no t uncertainty with a lead / lag ratio of 8.25 and will reach the trip setpoint at 6.74 seconds. Case 2 has a -3 percent I uncertainty for lead and a +3 percent t uncertainty for lag resulting in a le i/ lag ratio of 7.77. Case 2 will reach the trip setpoint at 7.25 seconds. Case 3 has a -10
L U.S. NRC November 12,1996 percent t uncertainty for lead and a +10 percent t uncertainty for lag resulting in a lead / lag ratio of 6.75. Case 3 will reach the trip setpoint at 8.57 seconds. Case 4 has the nominal lead / lag time constant with an additional lag component with time constant of 6 seconds in
).
_ the Tavg function of OTAT equation and reaches the trip setpoint at 14.04 seconds. Table I summarizes the time to trip for each of these cases. The additional lag time constant was set at 6 seconds in all applicable Braidwood and Byron UFSAR Chapter 15 accident analyses.
i' l
I Table 1. Summary of Lead / Lag time constant effect Case T4 T5 seconds to seconds Trip Time seconds seconds
- 1. Nominal Tech Spec 33 4
0 6.74
- 2. Tech Spec +/- 3%
32.01 4.12 0
7.25
- 3. Tech Spec +/- 10%
29.7 4.4 0
8.57
- 4. Safety Analysis
- 33 4
6 14.04
- In the actual safety analysis, the gain for the OTAT setpoint K is set at 1.5 versus the i
TS value of 1.325 to include all other deviations as described below.
- The OTAT calibration setpoint at Braidwood and Byron includes additional conservatisms similar to other protection setpoints. The calibrated setpoint includes allowances, where applicable, for process measurement accuracy, primary element accuracy, sensor calibration accuracy, sensor temperature effects, sensor pressure effects, sensor drift allowances,7300 rack calibration accuracy, measurement & test equipment accuracy, 7300 rack comparator setting accuracy,7300 rack temperature effects,7300 rack drift allowances, and appropriate environmental and bias allowances.
As illustrated in the above example, even though current Braidwood and Byron UFSAR Chapter 15 accident analyses do not explicitly include a i3 percent (Braidwood) or i10 percent (Byron) time constant deviation for the OTAT reactor trip function, an additional 6 second delay function (lag function to measured Tavg)in the accident analyses bounds this deviation. The actual performance of the Reactor Protection System (RPS) in the field resuhs in a trip of the reactor earlier than the FSAR accident analysis. This 1
methodology is consistent with current Westinghouse accident analysis methodology.
In summary, Comed agrees with the HICB analyses and conclusions and believes that Braidwood and Byron are being operated within their licensing bases and TS.
i U.S. NRC November 12,1996 1
Please address any comments or questions regarding this matter to Harry Pontious, Braidwood Nuclear Licensing Administrator, at (630) 663-7205.
j Sincerely, t
4 dfem John B. Hosmer
]
Engineering Vice President a
Attachments cc:
A. B. Beach, Regional Administrator - RIII R. R. Assa, Braidwood Project Manager - NRR G. F. Dick Jr., Byron Project Manager - NRR C. J. Phillips, Senior Resident Inspector - Braidwood S. D. Burgess, Senior Resident Inspector - Byron Office of Nuclear Facility Safety - IDNS 1
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Figure 1. OTAT Lead / Lag Time Constant Sensitivity T4=33 sec,23=4 sec for 30 seconds ramping 1.40 A..;
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0 Noramtized Delta-T Input
- - - - Case 1,14=33, t5=4,16=0 seconds (0% error)
- - - - - - Case 2, t4=32.01, tS=4.12, tS=0 seconds (3% error) ad
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- - - Case 3, t4=29.7 t5=4.4, t6=0 seconds (10% error)
Case 4, t4=33, tS=4, t6-1 seconds (0% error plus 6 sec lag on Tavg) 0.00 :
8 8 8 8 8, 8 8 8 8 8 8 8 8 8 8, 8 8 88 8 8 8 8 8 8 8 8 8 8 8 8 8 s e o n e e a e a s a a m e e a e a e ~ s, s M"
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i References 1.
Ramin R. Assa (NRC) letter to D. L. Farrar (Comed), " Request for Information -
Dynamic Testing of Instrumen_t Channels at Braidwood and Byron (TAC Nos.
t M95341 and M95340)," dated May 22,1996 2.
Teleconference between the United States Nuclear Regulatory Commission Staff and Commonwealth Edison Company regarding the Request for Information -
i Dynamic Testing of Instrument Channels at Braidwood and Byron held on June 21,1996 3.
WCAP-8745-P-A, " Design Bases foi the Thermal Overpower AT and Thermal.
1 Overtemperature AT Trip Functions," dated September,1986 i
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